lh6ch02water.ppt

8/18/2019 Lh6Ch02Water.ppt

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Chapter 2 :Water


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• What kind of interactions occur between dierenttype of molecules in water.

• Why water is a good medium for life

• Why nonpolar moieties aggregate in water

• How dissolved molecules alter properties of water

• How weak acids and bases behave in water: to beable to solve weak acid problems with theHenderson-Hasslebalch euation.

• How buers work and why we need them

• How water participates in biochemical reactions

Learning goals:


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!tructure


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"C#


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Common H-bonds inBiochemistry


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Some Biologically Important H-bonds


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H-bond Strength and Alignment


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Importance of Hydrogen Bonds

• !ource of uniue properties of water

• !tructure and function of proteins

• !tructure and function of $%&

• !tructure and function of polysaccharides

• 'inding of substrates to en(ymes• 'inding of hormones to receptors

• )atching of m*%& and t*%&

“I believe that as the methods of structural chemistry are further applied to

physiological problems, it will be found that the significance of the hydrogen

bond for physiology is greater than that of any other single structural feature.”

–Linus Pauling, The Nature of the Chemical Bond, 1939


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Water as a Solvent

+ Water is a poor solvent for nonpolar

substances, nonpolar gases

, aromatic moieties

, aliphatic chains

+ Water is a good solvent for chargedand polar substances

, amino acids and peptides

, small alcohols, carbohydrates


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t t


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o vat on an y rat on!pheres


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F t t t


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F c er ng usters an at rateCages


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he Hydrophobic !"ect• *efers to the association or folding of

nonpolar molecules in the aueous solution

• "s one of the main factors behind:

– protein folding

– protein-protein association

– formation of lipid micelles

– binding of steroid hormones to their receptors

• $oes not arise because of some attractive

direct force between two nonpolar

molecules


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! b ) $i l


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!ubstrates )ust $isplaceWater to 'ind #n(ymes


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Approximate Bond

Strength, kJ/mole

12-30

20


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Water Bound to Hemoglobin

%& p'ri(ied (rom )ater %& )ith *ater +emoed

#roton Hop and Hydronium


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#roton Hop and Hydronium


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Water Bound in a #rotein Channel $Cytochrome f%

Facilitates Proton

Hopping – see

later in

Photosynthesis


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&smotic #ress re


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&smotic #ressure

Cell 'esponse to &smotic #ressures


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Cell 'esponse to &smotic #ressures

#lants (se &smotic #ressure


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rote#tion Again"t *ind


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Ioni)ation of Water

Keq = [H+][OH-] / [H2O] = 1. ! 1"-1# $

%oncentration o& 'ater - one liter = 1("""g

$ole )t )ater = 1."1*

[H2O] = **.* $

K' = [H+][OH-] = Keq ! [H2O] = 1 ! 1"

-1 $2

&or p,re 'ater [H+] = [OH-]

so( [H+] = 1"- $

pH is negatie log [H+] ( &or p,re 'ater = ."


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Weak Acids

%A . % A-

e %A- / %A a

%ender"on-%a""el&al#h 5'ation +earrange" a

p% pa log 6 A- / %A 7

)hen pa p% 8 A- %A


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A


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W k id h di" K


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Weak acids have di"erent pK as


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n)ymes ave p op ma e a e o


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n)ymes ave p op ma e a e otheir Function


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Water as a 'eactant


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Water as a 'eactant


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1 liter o( 01 9 gl:#ine

a )hat p%;" i" gl:#ine a good &'((er d'e to it" amino

gro'p

roblem / in Chapter 2


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1 liter o( 01 9 gl:#ine

a *hat p% i" gl:#ine a good &'((er d'e to it" amino

gro'p

=%3

>l:#ine ?%2-?@@-

pa;" 234 and

So it )o'ld &e good /- 10 (rom ea#h pa

)hi#h )o'ld &e (rom 13 to 33 and .# to 1".# &or the

aino gro,p.

roblem / in Chapter 2


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C liter o( 01 9 gl:#ine

0 in a 01 9 "ol'tion, p% 0 )hat (ra#tion ha" the

amino gro'p a" –=%3 D

!aple o& a %licer 3,estion4 5-6H7+ is

8.H8

9.8-

%.H2O

:.H+

.OH-

roblem / in Chapter 2 6H7

+

;lycine = %H2-%OO-

pKa.#


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+

;lycine = %H2-%OO-

pKa.#C liter o( 01 9 gl:#ine

0 in a 01 9 "ol'tion, p% 0 )hat (ra#tion ha" the

amino gro'p a" –=%3D

p% pa log A/%A

0 log A/%A

log A/%A -0 A/%A 02$ 02$%A A

%A A 019 "o %A 02$%A 01 9 12$%A 019

"o %A 00E 98and that i" "? o( 019 "o

not a"ked A 002 9 or 20F


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+

;lycine = %H2-%OO-

pKa.#


c %o) m'#h $9 @% i" needed to #hange p% (rom

to 10 (or 1 Giter o( 019 gl:#ineD


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c %o) m'#h $9 @% i" needed to #hange p% (rom

to 10 (or 1 Giter o( 019 gl:#ineD

p% pa log A/%A 10 log A/%A

"o log A/%A 04 th'" A/%A 2$ 2$%A A

%A A 01 9 %A 2$ %A 01 9 3$%A 019

"o %A at p% 10 002 mole"/G

(rom p% %A i" #onerted to A &: adding @% -, that i" %A i"

lo)ered (rom 00E9 to 0029 or a #hange o( 00$1 mole"

00$1 mole"/$ mole"/G 001 G

10 ml o( $9 @%


+

;lycine = %H2-%OO-

pKa.#


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*hen F o( gl:#ine i" in it" –=%3 (orm, )hat i" the

p% o( "ol'tion d'e to it;" amino gro'pD 6('n#tionall:re)orded (rom the text7

p% pa log A/%A "o thi" i" ea": %A dominate", "o it )ill

&e on the a#id "ide o( the pa A i" onl: 1F or 001 "o the

log o( A/%A H -2 th'" p% – 2 or I


+

;lycine = %H2-%OO-

pKa.#

hings to *no+ and ,o Before


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hings to *no+ and ,o BeforeClass

1 >eneral ?hemi#al ropertie" o( *ater

2 p% de(inition and )hat it mean"ho) to #al#'late it

3 Strong " *eak A#id"

4 %ender"on-%a""el&al#h 5'ation and ho) to do#al#'lation" )ith it

$ *eak &ond" and their relatie &ond "trength

9ake "'re :o' are a&le to do O% Pro0les

#al#'lating p% 62-*( 7, p% a((e#t" "ol'&ilit: 617

and 'ptake o( a"pirin 61*7 and re"t on &'((er" 6117

he: are part o( ?la"" ?li#ker K'e"tion" and ?a"e

lh6ch02water.ppt

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